Can the controllers see each other on Layer 2? After you attempt to ping, from the CLI do:
# show arp
Can you see the MAC address of the other controller? Do the controllers share more then 1 VLAN? Can you ping the other controllers IP on the other VLANs?
If you have VRRP configured, can you confirm what the VRRP status is on both? If they cannot talk on L2 they should both be trying to be master?
On both controllers try:
# show vrrp stats all
What is the VR State on both controllers which should be connected by VRRP?
Is the port which the controllers are trying to sync over set to 'trusted'? Are any ACLs applied to the interface?
Thanks,
_ELiasz